Caster with weight transferring tab

ABSTRACT

The invention consists of a caster comprises a yoke having a weight transferring tab and a wheel with groove for receiving the tab. Preferably, the yoke and wheel are made out of plastic, and in some embodiments two different types of plastic. A tab and groove helps transfer the weight of the load on the castor away from the arms of the yoke and onto the wheel. In a preferred embodiment the plastic wheel is molded so as to include a shaft on either side that snap into receiving holes in the yoke, thus avoiding the need for separate axel and rivets.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 60/916,360, filed on May 7, 2007, which is incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was not developed with the use of any FederalFunds, but was developed independently by the inventor.

BACKGROUND OF THE INVENTION

Casters are well known in the furniture industry as a device forallowing furniture to roll across floors. Casters are a particularlycommon attachment to bed frames. Traditionally in order to withstand thepressure and weight of beds and people on the beds, the yoke of bedframe casters have been made from metal. In order to reduce cost andweight it is desirable that a caster be manufactured with plastic parts.

SUMMARY OF THE INVENTION

The invention comprises of caster comprised of a yoke with a weighttransferring tab and a wheel with groove for receiving the tab.Preferably, the yoke and wheel are made out of plastic, and in someembodiments two different types of plastic. A tab and groove helpstransfer the weight of the load on the castor away from the arms of theyoke and onto the wheel. In a preferred embodiment the plastic wheel ismolded to include a shaft on either side that snaps into receiving holesin the yoke, thus avoiding the need for separate axel and rivets. In apreferred embodiment the invention includes a bed frame comprised ofsupport members for supporting a bed attached to the caster describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top perspective view of the caster of the presentinvention assembled.

FIG. 2 shows a top perspective view of the caster of the presentinvention unassembled.

FIG. 3 shows a bottom perspective view of the caster of the presentinvention unassembled.

FIG. 4 shows a partial cross sectional view of a bed frame and bed withthe caster of the present invention attached.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 2 and 3 show a caster 1 comprising a stem 2, a yoke 4 and awheel 6. The stem 2 is used to connect to the caster 1 to a piece offurniture (not shown), preferably a bed, although it may be attached toany object including other types of furniture. The stem 2, preferablymade out of metal or plastic, connects the caster to the yoke 4 via ahole 16 in the top of the yoke 4. In the preferred embodiment the stem 2snaps into the hole 16 through pressure.

When using the term “caster” in this application it is meant to refer toeither the combination of the stem 2, yoke 4 and wheel 6, or just theyoke 4 and the wheel 6 (without a stem).

The yoke 4 is preferably made out of a single piece of plastic formedthrough injection molding. The yoke comprises a top portion 18 and twoarm portions 20 extending downwardly from the top portion 18 forsupporting the wheel 6. The yoke 4 contains a stem attachment hole 16 inthe top portion 18 as well as wheel attachment holes 14 on each of thearms 20. The underside of the top portion 18 of the yoke 4 has a tab 12that extends downwardly from the underside of the top portion 18 thatfits into a groove 8 formed in the wheel 6.

In one preferred embodiment the top portion 16 of the yoke 4 hasintegrally formed ribs 24. These ribs provide additional strength andreduce cost by decreasing the required thickness of the yoke 4 therebyreducing the total quantity of plastic required.

The wheel 6 is preferable made out of a single piece of plastic formedthrough injection molding. The wheel is substantially cylindrical andhas a groove 8 running around its center (coaxially with its axis ofrotation). The groove 8 is designed to receive the tab 12. Preferablythe wheel 6 has shafts 10 extending on either side about which the wheelrotates when the shafts 10 are snapped into place in the wheel receivingholes 14 of the yoke 4. The wheel 6 may be solid or hollow. The shafts10 are preferably integrally formed as part of the wheel throughinjection molding. The shafts 10 serve as a hub or axis of rotation forthe wheel 6.

The shafts 10 may be hollow or solid. In one preferred embodiment thecaster 1 is assembled without any axel. This reduces cost and weight asneither axel or axel attachment hardware (such as rivets or screws) arerequired. In another embodiment an axel (not shown) may be added eitherthrough the shafts 10, if they are hollow, or instead of the shafts.

In a preferred embodiment the ends of the yoke arms 20 have a beveledarea 22 leading to the wheel receiving holes 14. This helps guide theshafts 10 into the wheel receiving holes 14, making it easier to snapthe wheel 6 into place in the yoke 4. Preferably the length of theshafts 10 is just slightly longer than the distance between the tworeceiving holes 14. Thus when the wheel 6 is slid into place, the arms20 are pushed out slightly by the shafts 10. When the shafts 10 reachthe holes 14, the arms 20 snap back into normal position leaving thewheel 6 held securely in place.

In use, the caster 1 is transfers the weight of the bed (or otherfurniture item) through the stem 2 and the tab 12 onto the wheel 6relieving the yoke arms 20 of a large portion of the weight bearingload, thus allowing the yoke 6 to be made from a less strong naturedthan metal, such as plastic.

In the preferred embodiment the yoke 4 and wheel 6 are manufactured fromdifferent types of plastic. Preferably, the plastics are selected sothat the coefficient of friction between the tab 12 and the wheel 6 isless than the coefficient of friction between the wheel 6 and the flooracross which it will roll. This balance ensures that the caster 1 rollseasily when loaded with a mattress and boxspring.

In one preferred embodiment the yoke 4 is fabricated from a glassreinforced nylon material and the wheel is fabricated from an impactresistant polypropylene material.

In one embodiment the caster 1 further comprises a braking mechanism(not shown) to prevent the castor from rolling when the brake is in thelocked position.

In another preferred embodiment the brake is not a separate part of thecaster. However, the caster 1 is designed so that the tab 12 acts as abrake. Under unloaded conditions the tab 12 does not touch (or barelytouches) the wheel 6. When under an expected load the yoke 4 bendssufficiently so that the tab 12 presses more firmly against the wheel 6,thereby acting as a brake. In the case of a caster 1 for use with a bed,the yoke 4 is designed, in this preferred embodiment, so that under theweight of only a bed and box frame the tab 18 does not touch (or barelytouches) the wheel 6 and no significant force is applied to the wheel 6allowing the caster to roll freely. When a person is on the bed, theadditional load causes the yoke to bend sufficiently so that the tab 18presses against the wheel 6, thereby acting as a brake and preventing orsignificantly reducing the ability of the caster to roll.

In another embodiment the yoke 4 or the wheel 6 may be made out ofhardened rubber instead of plastic. Likewise the stem 2 may be made outof any sufficiently strong material, such as plastic or hardened rubber,instead of metal.

In operation when weight is placed on the stem 2 this weight istransferred to the yoke 4. In prior art embodiments, the great majorityof the weight (of a bed or other item to which the caster is attached)was placed on the arms 20 of the yoke just above the holes 14 at thepoint where the arms 20 meet the shafts 10 or axle. Thus, in the priorart, the caster often failed by the arms bending or the shafts bending.Another failure mode of the prior art was for the yoke top 18 to benddown and interfere with the wheel. In the present invention, the tab 12transfers a great portion of the weight directly onto the wheel 6, thusrelieving stress on the arms 20. The use of a groove 8 in the wheel 6provides a guide for the tab 12 and prevents lateral forces on the tabfrom becoming too great. The groove also allows the force of the weighttransferring through the stem 2 to be placed closer to the center ofrotation of the wheel 6 and not on the surface of rotation of the wheel6. This makes the caster easier to roll under weight. However, in oneembodiment of the invention the caster is made without a groove 8.

Exemplary Embodiment and Tests

The following embodiment is exemplary and the dimensions described arenot intended to limit the scope of the invention. Likewise the testsdescribed are not meant to be requirements or limitations of theinvention.

In one embodiment that the inventor has found to be particularly usefulwhen the yoke is made of glass reinforced nylon and the wheel isfabricated from impact resistant polypropylene. The yoke 4 measures 2.00inches from the inside of one arm 20 to the inside of the opposite arm20. The thickness of the tab 18 is 0.116 inches. The wheel 6 measures1.94 inches across and the groove 8 has a width of 0.146 inches. Thediameter of the wheel 6 at the bottom of the groove 8 is 1.298 inches.Each shaft extends 0.21 inches beyond the wheel and has a diameter of0.370 inches. The tab 18 is of a length such that when the wheel 6 isassembled into the yoke 4, and the caster is not under load, the spacebetween the end of the tab 18 and the bottom of the groove 8 is0.005-0.010 inches.

A caster made in accordance with these dimensions was fabricated andtested by the inventor. Ten casters were tested and withstood a 660 lbstatic load test (five times their rated weight) for one minute. Twocasters also passed a static load test at 660 lbs of pressure for 24hours (considered an extreme condition and for outside normal operatingconditions to the intended application).

As has been discussed above, in one preferred embodiment the caster 1 isattached to a bed frame/support member 26 for supporting a bed 28 asshown in FIG. 4. In this embodiment the bed frame is likely to includefour casters 1, one at approximately each corner.

While the caster of the present invention was designed for use with abed frame, the same design may be applied to any caster.

The particularly embodiment described herein is provided by way ofexample and is not meant in any way to limit the scope of the claimedinvention. It is understood that the invention is not limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. Without further elaboration, the foregoingwill so fully illustrate the invention, that others may by current orfuture knowledge, readily adapt the same for use under the variousconditions of service.

1. A caster comprising: a yoke having a weight transferring tab; a wheelbeing rotatably attached to the yoke, the wheel having a groove forreceiving the weight transferring tab, wherein the tab transfers theweight of a load applied to the yoke to the groove, applying africtional braking force to the wheel thereby functioning as a brake. 2.The caster of claim 1 wherein the yoke or wheel is made of plastic. 3.The caster of claim 1 wherein the wheel is made of polypropylene and theyoke is made of glass reinforced nylon.
 4. The caster of claim 1 furthercomprising a stem, the stem being made of metal or plastic, the stembeing connected to the yoke.
 5. The caster of claim 1 wherein when thecaster is under loaded conditions the yoke bends so that the tab pressesagainst the groove thereby functioning as a brake.
 6. The caster ofclaim 1 wherein the yoke is capable of supporting at least about 500pounds of weight applied to the caster.
 7. The caster of claim 1 whereinthe yoke is capable of supporting at least about 660 pounds of weightapplied to the caster.
 8. The caster of claim 1 further comprising astem connected to the yoke, the stem receiving the weight of the loadapplied the caster, and the weight being transferred from the stem tothe tab.
 9. The caster of claim 8 wherein the stem is disposedsubstantially on a centerline of the yoke and wherein the tab transfersthe load applied to the stem directly to the groove.
 10. The caster ofclaim 1 wherein the groove further comprises a bottom and the weightbearing tab contacts the bottom of the groove thereby applying thefrictional braking force thereto.
 11. A caster comprising: a yoke havinga top portion, a pair of arms extending downwardly from the top portionand a weight transferring tab extending downwardly from the top portion;a wheel being rotatably supported between the pair of arms, the wheelhaving a groove for receiving the weight transferring tab, wherein thetab transfers the weight of a load applied to the yoke to the groove,applying a frictional braking force to the wheel thereby functioning asa brake.
 12. The caster of claim 11 wherein the tab is locatedsubstantially on a centerline of the yoke and the grove is locatedsubstantially on a centerline of the wheel and wherein the tab transfersthe load applied to the yoke to the groove.
 13. The caster of claim 11wherein the yoke is capable of supporting at least about 500 pounds ofweight applied to the caster.
 14. The caster of claim 11 furthercomprising a stem connected to the yoke, the stem receiving the weightof the load applied the caster, and the weight being transferred fromthe stem to the tab.
 15. The caster of claim 24 wherein the stem isdisposed substantially on a centerline of the yoke and wherein the tabtransfers the load applied to the stem directly to the groove.
 16. Thecaster of claim 11 wherein when the caster is under loaded conditionsthe yoke bends so that the tab presses against the groove therebyfunctioning as a brake.
 17. The caster of claim 13 wherein the yoke orwheel is made of plastic.
 18. The caster of claim 11 wherein the yoke iscapable of supporting at least about 660 pounds of weight applied to thecaster.
 19. The caster of claim 11 wherein the groove further comprisesa bottom and the weight bearing tab contacts the bottom of the groovethereby applying the frictional braking force thereto.
 20. A caster forsupporting a loaded bed comprising: a yoke having a top portion, a pairof arms extending downwardly from the top portion and a weighttransferring tab extending downwardly from the top portion, the yokebeing fabricated from a plastic material, the yoke being capable ofsupporting at least about 500 pounds of weight applied to the caster bythe bed; a wheel being rotatably supported between the pair of arms, thewheel having a groove for receiving the weight transferring tab, thewheel being fabricated from a plastic material; wherein the tabtransfers the weight of a load of the bed applied to the yoke to thegroove, applying a frictional braking force to the wheel therebyfunctioning as a brake;
 21. The caster of claim 20 wherein the tab islocated substantially on a centerline of the yoke and the grove islocated substantially on a centerline of the wheel and wherein the tabtransfers the load applied to the yoke to the groove.
 22. The caster ofclaim 20 further comprising a stem connected to the yoke, the stemreceiving the weight of the bed applied the caster, and the weight beingtransferred from the stem to the tab.
 23. The caster of claim 22 whereinthe stem is disposed substantially on a centerline of the yoke andwherein the tab transfers the load of the bed applied to the stemdirectly to the groove.
 24. The caster of claim 20 wherein when thecaster is under the load of the loaded bed the yoke bends so that thetab presses against the groove thereby functioning as a brake.
 25. Thecaster of claim 20 wherein the yoke is capable of supporting at leastabout 660 pounds of weight applied to the caster.
 26. The caster ofclaim 20 wherein the groove further comprises a bottom and the weightbearing tab contacts the bottom of the groove thereby applying thefrictional braking force thereto.